1. Field of the Invention
The present invention is directed to an imaging apparatus used in an image forming apparatus such as a facsimile apparatus, etc. More particularly, the present invention is directed to an imaging apparatus which includes a separating unit and a reading unit.
2. Discussion of the Background
An imaging apparatus for reading an original document is disclosed in Japanese Laid-Open Patent No. 1-271330. The imaging apparatus disclosed in this document includes a separating unit and a reading unit. In the separating unit, sheets of an original document placed on an original document table are separated one sheet by one sheet. In the reading unit, sheets of the original document which have been separated in the separating unit are read and then discharged.
In this background device operations in both the separating unit and reading unit are controlled by the same one motor. In this background device the original document to be read is transported at a predetermined speed based on an image reading resolution of a sensor in the reading unit. Transporting of the original document is stopped if a capacity of a memory for storing image data during reading of the original document is exceeded.
For these reasons, a stepping motor is typically used as the one motor controlling both the separating unit and the reading unit. In a typical stepping motor utilized in such a device, which may be a two-phases hybrid type, torque decreases around 2000 pps (pulse per second)--3000 pps, and a maximum speed is 3500 pps.
A high performance in reading the original document is now required, and as a result the stepping motor is driven with a large current and heavy torque. However, this results in an increase in vibration, noise, and heat generated from the stepping motor.
In the separating unit, a driving load of a transporting roller is larger than that of a separating roller. As a result, a load fluctuation occurs when the original document is separated from the separating roller. Such a load fluctuation may be transmitted to a shaft of the stepping motor, which thereby causes uneven rotation in the stepping motor. In such an imaging apparatus equipped with only one stepping motor, the load fluctuation from the separating unit is transmitted to rollers in the reading unit, which thereby results in the reading unit not correctly reading image data.